1. Field of the Invention
The present invention relates to an inverted F-type antenna apparatus and a potable radio communication apparatus provided with the inverted F-type antenna apparatus, and in particular, to an inverted F-type antenna apparatus for portable radio communication apparatuses mainly for mobile communications, such as a portable telephone, and to a portable radio communication apparatus provided with the above-mentioned inverted F-type antenna apparatus.
2. Description of the Prior Art
In recent years, a mobile communication system using portable radio communication apparatuses, such as a portable telephone, has been rapidly developed. This portable telephone has been changed from the positioning thereof as a conventional audio terminal apparatus to an information terminal apparatus for performing transmission of data and images. In accordance with this, a folding type portable telephone, which is more suitable for increasing the size of the screen, has been widely used.
FIG. 31A is a plan view showing a construction of a portable radio communication apparatus 1001, which is a straight type portable telephone according to a prior art, and FIG. 31B is a plan view schematically showing a construction of a dielectric substrate 1004 provided with an inverted F-type antenna apparatus 1005 of FIG. 31A.
Referring to FIG. 31A, a liquid crystal display section 1003 is provided near the upper side of the center portion of a housing 1002 of the portable radio communication apparatus 1001, while a dielectric substrate 1004 is provided throughout the entire space inside of the housing 1002. In this case, the built-in antenna 1005 is arranged above the dielectric substrate 1004. As shown in FIG. 31B, this built-in antenna 1005 is constructed of a rectangular flat-plate-shaped antenna element 1006, a columnar pin-shaped short-circuit conductor 1007 for connecting the antenna element 1006 with a grounding conductor (not shown) and a columnar pin-shaped feeding conductor 1008 for connecting the antenna element 1006 with a feeding coaxial cable (not shown) at a feeding point. The built-in antenna 1005 is normally constructed of a low-height small-size inverted F-type antenna apparatus called a planar inverted F antenna (PIFA). This inverted F-type antenna apparatus, which is an unbalanced type antenna, therefore operates as an antenna with a large current flowing through the grounding conductor formed on the rear surface of the dielectric substrate 1004. In this case, current standing waves are generated when a dimension obtained by adding the length in the direction of the longer side of the grounding conductor to the length in the direction of the shorter side of the grounding conductor is greater than xc2xc with respect to the wavelength 1 of the frequency band of the radio wave which is used, and therefore, a wideband characteristic can be obtained.
However, in the case of the built-in inverted F-type antenna apparatus of the folding type portable radio communication apparatus, the dimension of the dielectric substrate, i.e., the dimension of the grounding conductor is disadvantageously reduced in comparison with that of the built-in inverted F-type antenna apparatus of the straight type portable radio communication apparatus 1001. In this case, when the frequency band of the radio wave which is used is comparatively low, the dimension obtained by adding the length in the direction of the longer side of the grounding conductor and the length in the direction of the shorter side of the grounding conductor becomes smaller than xc2xc with respect to the wavelength 1 of the frequency band of the radio wave which is used. Consequently, there has been such a problem that the grounding conductor stops contributing to the excitation of the antenna, disadvantageously leading to a narrow-band characteristic.
An object of the present invention is to solve the aforementioned problems and provide an inverted F-type antenna apparatus which is built in a folding type portable radio communication apparatus, the antenna apparatus being capable of achieving a comparatively wideband characteristic even when the frequency band of the radio wave which is used is comparatively low and the grounding conductor does not contribute to the excitation of the antenna, as well as a portable radio communication apparatus that employs the antenna apparatus.
Another object of the present invention is to provide an antenna apparatus which is built in a folding type portable radio communication apparatus, the antenna apparatus being capable of reducing the influence from a human body and reducing the radiation loss of the antenna apparatus, as well as a portable radio communication apparatus that employs the antenna apparatus.
In order to achieve the aforementioned objective, according to one aspect of the present invention, there is provided an inverted F-type antenna apparatus including a grounding conductor, an antenna element arranged on the grounding conductor so as to face the grounding conductor, and at least one coupling element provided between the grounding conductor and the antenna element so as to face the grounding conductor and the antenna element. The inverted F-type antenna apparatus further includes first connection means for electrically connecting the antenna element with the grounding conductor at least in one place.
In the above-mentioned inverted F-type antenna apparatus, the grounding conductor, the antenna element and the coupling element are arranged so as to be substantially parallel to each other.
In the above-mentioned inverted F-type antenna apparatus, the antenna element and the grounding conductor are preferably arranged so that a distance between the antenna element and the grounding conductor in an end portion where the antenna element and the grounding conductor are electrically connected with each other by the first connection means is different from a distance between the antenna element and the grounding conductor in another end portion located opposite to the end portion.
In the above-mentioned inverted F-type antenna apparatus, the coupling element is preferably arranged so as to be inclined with respect to the grounding conductor.
In the above-mentioned inverted F-type antenna apparatus, the antenna element preferably has a shape curved along a configuration of a housing for accommodating the inverted F-type antenna apparatus.
In the above-mentioned inverted F-type antenna apparatus, at least one of the coupling element and the antenna element is preferably provided with a bent portion.
In the above-mentioned inverted F-type antenna apparatus, the grounding conductor is preferably provided with a bent portion.
In the above-mentioned inverted F-type antenna apparatus, a length of a sum total of lengths of two mutually different sides of the grounding conductor is preferably equal to or smaller than a quarter of a wavelength corresponding to a lowest frequency band among frequency bands which are used by a portable radio communication apparatus that employs the inverted F-type antenna apparatus.
The above-mentioned inverted F-type antenna apparatus preferably further includes second connection means for electrically connecting the antenna element with the coupling element at least in one place.
In the above-mentioned inverted F-type antenna apparatus, a connecting point of the second connection means is preferably arranged near a connecting point of the first connection means.
In the above-mentioned inverted F-type antenna apparatus, dimensions of the antenna element and the coupling element are preferably set so that the connecting point of the second connection means is located substantially in a portion of an anti-node of a current standing wave generated in the antenna element and the coupling element, and the coupling element operates as a quarter-wave length resonator when the inverted F-type antenna apparatus is excited by a radio signal of a predetermined wavelength.
In the above-mentioned inverted F-type antenna apparatus, the antenna element and the coupling element are preferably electrically connected with each other by a common feeding conductor.
In the above-mentioned inverted F-type antenna apparatus, the antenna element and the coupling element are preferably electrically connected with each other by a common short-circuit conductor.
In the above-mentioned inverted F-type antenna apparatus, a resonance frequency of the inverted F-type antenna apparatus is preferably adjusted by forming a slit in the antenna element.
In the above-mentioned inverted F-type antenna apparatus, a resonance frequency of the inverted F-type antenna apparatus is preferably adjusted by forming a slit in the coupling element.
In the above-mentioned inverted F-type antenna apparatus, a resonance frequency of the inverted F-type antenna apparatus is preferably adjusted by forming a slot in the antenna element.
In the above-mentioned inverted F-type antenna apparatus, a resonance frequency of the inverted F-type antenna apparatus is preferably adjusted by forming a slot in the coupling element.
In the above-mentioned inverted F-type antenna apparatus, an amount of electromagnetic coupling between the antenna element and the grounding conductor is preferably adjusted by changing an area of at least one of the antenna element and the coupling element.
In the above-mentioned inverted F-type antenna apparatus, a dielectric is preferably filled in either one of a part of internal portion and the whole portion of the inverted F-type antenna apparatus.
In the above-mentioned inverted F-type antenna apparatus, dimensions of the antenna element and the coupling element are preferably set so that the inverted F-type antenna apparatus resonates in a plurality of frequency bands.
According to another aspect of the present invention, there is provided a portable radio communication apparatus including an upper housing, a lower housing, a hinge portion for coupling the upper housing with the lower housing, and the above-mentioned inverted F-type antenna apparatus. In the portable radio communication apparatus, the inverted F-type antenna apparatus is arranged inside of the upper housing.
The above-mentioned portable radio communication apparatus preferably further includes a monopole antenna.